I’m doing some work for a client. He has a model railroad and wants to have a gantry crane he can operate with joysticks. He purchased this thing called an Arduino and needs me to program it for him.
Ok, I look up Arduino and think ‘no problem.’ The language for an Arduino is similar in style to C, so I can deal with it. He has 3 stepper motors, 3 ‘easy driver’ boards that control the motors, a joystick and an Arduino UNO to program it.
First thing we do is go through some tutorials, making an led light turn on, displaying the ambient temperature from a temp sensor and a few things like that. Then we figure out the wiring required to run the stepper motor through the easy drivers. It was late so he says he’ll solder them up and we can test next time.
Next time comes and the motors don’t move. I check the wiring and it looks right. all the wires have continuity from board to board, I power everything up and the power lights work. I used sample code from the easy driver designer’s website so that should work, but I get nothing.
So I check the specs on the motors. 3V, 1.7A, 400 steps/rotation. I’m feeding it power via the usb port on the Arduino which means I’m only giving it 0.5A. That’s the problem. So i get a separate power supply and feed it up to 2A. At this point I’m only testing 1 of the motors.
Still nothing. It’s only drawing about 0.035A. I check everything I can think of – make sure the motor is wired correctly, the boards are wired right, etc. I even try the other boards in case one of them got blown somehow.
Nothing.
Ok, I sign up on an arduino forum, post a question and call it a night to wait for an answer. The next day the client calls me and says to call this phone number and maybe the tech support people can help because that’s where he got the hardware from. I call them up and the tech. points me to their custom support page for stepper motors and the easy driver board. The instructions say to feed the motor at least 8V, but no more than 32V. 8V? But I have a 3V motor.
I go to the client’s workshop, set the power supply to 9V, 2A and separate the power to the Arduino from the power to the motors because the Arduino needs 3.3v or 5v, not 9v and I don’t want to blow it.
I power everything up and the motor starts to move. What? That’s all it needed? We wasted 3 hours because a 3V motor isn’t a 3V motor, it’s a 9V motor. There’s got to be some logic there, but I can’t figure it out.
I adjust the potentiometer on the easy driver board until the motor runs smoothly and watch it go for a min. Then it starts to miss. So I turn up the power a little more and my fingertip briefly touches the chip that controls everything and OUCH! That’s HOT! I don’t mean a little warm, but blisteringly hot. I swear the magic smoke is about ready to come out. (I’ll tell you about the magic smoke in computers some other day). I quick turn off the power and let it cool down a min.
I turn it back on and it runs smoothly, for 30 sec or so, then it starts missing again so I feel the chip again. Not as hot but getting hotter by the second. Something’s not right. I turn the pot down to the lowest setting that lets the motor run smoothly and it still starts missing after a min. Yep, the chip is sizzling again.
I call the tech guy again and he says that the easy driver is only good to about 1.2A but there is a driver board that can take up to 3A. Why did they sell a 1.2A board with a 1.7A stepper motor??? So the client orders the 3A boards and we’re waiting for them to arrive.
All that — a 3V motor that really needs 9V and the easy driver board can’t handle the amperage of the motor. All in a day’s work, I’m sure but, “Aaaaaarrrrrrrgggggggghhhhhh!!!!!”